Ossian Offshore Wind Farm, Scotland

Ossian is expected to produce first power before the end of the decade. Once complete, the project will be capable of powering almost 6 million Scottish homes and offsetting up to 7.5 million tonnes of carbon emissions per year.

Ossian Wind Farm Location and Site details

The offshore wind project is being developed within the E1 Plan Option (PO) Area awarded by Crown Estate Scotland (CES) as part of the ScotWind Leasing Round.

At 858km² of seabed, Ossian is one of the largest lease areas to be offered by the leasing round.

The location, which lies at average water depth of 72m, is approximately 84km off the east coast of Scotland and around 80km south-east of Aberdeen, Scotland.

Ossian Offshore Wind Farm details

The Ossian Offshore Wind array will include up to 270 wind turbines and up to six Offshore Substation Platforms (OSPs) with fixed bottom foundations or associated floating support structures and foundations.

The project infrastructure will also include moorings and anchoring systems for each floating substructure; a dynamic/static inter-array cable network connecting individual wind turbines to OSPs and interconnector cables and between OSPs; and other ancillary components.

The final number of turbines for the project will be determined following environmental and engineering survey results, and based on individual wind turbine capacities.

The turbines will have a maximum rotor diameter of up to 350m and maximum blade tip height of up to 399m above Lowest Astronomical Tide (LAT).

The turbines will be supported by floating substructures with mooring and anchoring systems to maintain position.

Semi-submersible and Tension-Leg Platform are being considered as floating substructures for the project. For mooring- catenary, semi taut, and taut mooring lines configurations are being evaluated.

The maximum number of mooring lines and anchors per foundation will be nine.

The OSPs will convert electricity to a higher voltage to enable efficient transmission directly to shore or grid network. The expected maximum dimensions of the topside of OSP will be 130m (length) by 110m (width), with a height of approximately 70m (above LAT).

The OSPs will be based on fixed jacket foundations with up to eight legs. These offshore platforms are expected to have floating foundations, which will be fixed to the seabed with up to nine mooring lines per foundation anchored to the seabed.

All the foundations will have scour protection to prevent seabed erosion and ‘scour hole’ formation around anchor and mooring systems, and foundation structures.

The cable network including inter-array cabling linking the individual wind turbines to OSPs, and interconnector cables between OSPs will total approximately 1,515km.

The Ossian Offshore Wind Farm’s proposed offshore export cable corridor(s) and proposed onshore export cable corridor(s) including landfall location(s) will be made available following the conclusion of the Offshore Transmission Network Review (OTNR) and National Grid Holistic Network Design Follow Up Exercise (HNDFUE) review.

Contractors involved

Consulting and engineering services provider RPS led the Offshore Environmental Impact Assessment (EIA) for the Ossian Offshore Wind farm array.

HiDef Aerial Surveying conducted digital aerial surveys across the Ossian array area from March 2021 to February 2023. The survey took 330 hours of flight time covering an area of 4,050km².

In March 20223, the project partners awarded the contract for geotechnical investigations to Fugro and Ocean Infinity. Fugro will use its geotechnical drilling vessel the Fugro Scout for the contract works, while Ocean Infinity will use its multi-purpose support vessel Stril Explorer.

The scope of works for Fugro includes downhole geotechnical sampling and in situ cone penetration testing. On the other hand, Ocean Infinity will focus on the seabed scope including shallow vibro-cores and deep push seabed cone penetration tests.